A throttle valve opening ratio sensor for gasoline engines uses a potentiometer system to detect the rotation angle (mechanical angle) of the throttle valve almost within 90°. The potentiometer system uses a brush attached to a rotating shaft of the valve and a fixed resistor, the brush rotating with the shaft sliding the resistor to provide changing resistance between the brush and an end of the resistor, from which the rotation angle of the valve is determined. Though the potentiometer system has a simple circuit, its signal is unstable because of the change of the sliding part with time. Thus proposed is a non-contact-type angle sensor for detecting the rotation angle of a shaft by measuring the direction of a magnetic flux generated from a magnet fixed to the rotating shaft by a magnetic sensor.
JP 2008-281556 A discloses an angle detection apparatus comprising a magnet rotor having a two-pole magnet, and a magnetic sensor for detecting the direction of a magnetic flux generated from the two-pole magnet; the two-pole magnet being magnetized in a direction perpendicular to the rotation axis of the magnet rotor; the magnetic sensor comprising a magnetosensitive plane having pluralities of spin-valve, giant-magnetoresistive devices each having a pinned layer having a fixed magnetization direction and a free layer having a magnetization direction rotating in response to the magnetic flux direction; and the magnetic sensor being arranged relative to the magnet rotor, such that the magnetosensitive plane crosses the magnetic flux, with perpendicular magnetic flux density components having different amplitudes on the magnetosensitive plane. Having high sensor output linearity, this angle detection apparatus can detect the rotation angle with high accuracy. However, because it is required to detect a smaller rotation angle with high accuracy, the output linearity should be further increased.
JP 7-119619 B discloses an angle sensor comprising a permanent magnet attached to a shaft to be detected via a holding member, and magnetoresistive devices mounted on the holding member to oppose with a predetermined gap to detect a magnetic field of the permanent magnet, thereby determining the rotation angle of the shaft to be detected; the permanent magnet and the magnetoresistive devices being arranged only in a particular radial direction of the shaft to be detected. However, this angle sensor detects the magnetic field intensity, but does not detect the direction of the magnetic flux, failing to measure the rotation angle or movement with high accuracy.
As described above, because conventional apparatuses for detecting rotation angle or movement do not have sufficiently high output linearity necessary for high precision, it is desired to provide them with higher accuracy. In addition, in applications having limited space, such as camera lens barrels, it is also desired to miniaturize apparatuses for detecting rotation angle or movement distance with high accuracy.